EFFECT OF P-DELTA

[swelm]

HI

i made high rise buidling in etab programm with high 100 meter but i found this massage in the analysis file


CURRENT P-DELTA ANALYSIS ITERATION = 1
MAXIMUM NUMBER OF ITERATIONS ALLOWED = 2

CURRENT DISPLACEMENT MAGNITUDE = 0.044349
RELATIVE DISPLACEMENT CHANGE = 0.001288
RELATIVE DISPLACEMENT TOLERANCE = 0.001000

ITERATION DID NOT CONVERGE


so i want to ask if that nesscssary to change the relative displacement tolerance or want can i do?


thanks for all comments

 

[UcfSE]

What have you tried so far to figure this out yourself?

 

[271828]

The first thing you should do is approximate the P-Delta effects using manual methods. If your building is mostly translating (not twisting a great deal), then you should be able to get reasonable close using the standard approximate methods. Otherwise something's wrong.

 

[JAE]

Usually when Pdelta analyses don't converge, it's due to the structure not being stiff enough.

 

[haynewp]

What did the second iteration give? You only posted the first iteration data. Increase iterations allowed and post result.

 

[archeng59]

usually, at least 3 iterations are required for convergence. I use STAAD for P-Delta analyses.

 

[swelm]

i used 3 iterations but i found that massage again
( ITERATION DID NOT CONVERGE) because the relative displacement more than the tolerance displacement


so i increase the tolerance but i do not know if that right way or i should to calcuale the tolerance before i start calcualtion.

 

[shin25]

swelm,

have you checked if your relative displacement value is within the code prescribed maximum?

 

[UcfSE]

Try increasing the stiffness of the structure. Perhaps what you have does not work.

 

[271828]

I'll re-iterate: It should take very little time (30 min. max) to manually estimate the P-Delta effects. I think you owe it to yourself to do this. Modifying the structure until "it works" is insufficient IMO--just like kluging a computer program.

 

[J1D]

Swelm,
Do an Integrity Check if the program does it. And Do a linear static analysis first to see if the deflection is exceeding under say wind. Then check the specification you did for the P-Dalta analysis type (I don't kow ETAB well).